1. Field of the Invention
The present invention generally relates to the formation of patterns on semiconductor substrates and more specifically to a method of forming masks, such as chrome masks on quartz, with a reduced defect rate.
2. Description of the Related Art
Conventional systems utilize positive tone resist materials, including, but not limited to, high polymer organic films or negative resists materials including, but not limited to, high polymer organic films. A pattern is exposed on the positive or negative resists using an electromagnetic source, such as a laser beam or electron beam. When the positive resist is developed the exposed portions become soluble and are removed with a solution such as an alkaline or solvent solution. Similarly, when the negative resist is developed the unexposed portions become soluble and are removed with a solution such as an alkaline or solvent solution. Therefore, as is well known to those ordinarily skilled and the art, a positive or negative image of a pattern can be formed in a resist according to most design requirements.
However, opaque defects sometimes occur when patterning and exposing the negative resist when foreign material resides within the resist film or foreign material remains on the substrate after processing. Similarly, clear defects sometimes occur when forming the positive resist when foreign material resides on or in the resist film or a concentrated develop chemical attacks the resist.
Such defects result in improperly formed or etched patterns. For example, if the resist is used as a protective mask in an etching process, the clear or opaque defect would cause, respectively, too much or too little etching of the underlying layer of material to be patterned.
For example, as shown in FIG. 1, a linear edge 10, 11, 12 was intended to be formed. However, a defect 13 caused the linear edge to deviate from the intended line 12. Such a defect is considered repairable because the portions of the edge 11 and 10 can be easily connected (e.g., extended) to formed the missing line 12.
FIG. 2 illustrates non-repairable defects. More specifically, an area 21 of a pattern 20 and an edge 22 of a pattern 23 were not properly formed. The areas 21 and 22 should have been completed along the dotted lines shown in FIG. 2. These defects are non-repairable because, without knowing the dotted line patterns 21 and 22, it is not possible to accurately estimate the shape of the complete patterns 20 and 23. For example, one possible repair of the missing patterns would incorrectly connect patterns 23 and 20 along straight lines beginning in the opening in pattern 23.
If a defect is repairable, the pattern is copied from adjacent fields using the adjacent fields as a template. However, if the defect is non-repairable, such as that shown in FIG. 2, the item being manufactured will need to be scrapped or the entire pattern reworked, which substantially decreases production efficiency.
The invention described below substantially reduces the possibility of non-repairable defects and, therefore, dramatically increases production efficiency, lowers costs and increases reliability.